The present invention relates to a technique for printing images by forming dots on a print medium during main scanning, and more particularly to a technique for adjusting recording position misalignments in the direction of main scanning and reducing the graininess of images printed in color.
Color printers of the type in which inks of several colors are ejected from a head are currently used on a wide scale as computer output devices. Such color printers include those in which images are printed by ejecting ink drops from nozzles to form dots on a print medium during main scanning.
Printing systems can be divided into unidirectional printing systems in which images are printed only during the forward or reverse pass of a main scan, and bidirectional printing systems in which images are printed during both forward and reverse passes. Many of the contemporary color-ink jet printers utilize both unidirectional and bidirectional printing.
In a printing operation in which ink drops are ejected from nozzles to form dots on a print medium, the recording positions of the dots sometimes become misaligned due to the backlash of the drive mechanism for main scanning, the warping of the platen that supports the print medium from below, and the like. The method disclosed in JP 5-69625A, which has previously been filed by the present applicant, is known as an example of a technique aimed at preventing such misalignments. According to this conventional technique, adjustment values designed to cancel out dot formation misalignments in the direction of main scanning are recorded in advance, and recording positions are corrected on forward and reverse passes on the basis of these adjustment values.
Correcting dot formation misalignments in this manner can be used not only to correct misalignments between forward and reverse passes during bidirectional printing, but also to correct misalignments among dots of different color nozzles during unidirectional printing.
Conventional techniques for correcting dot formation misalignments were primarily aimed at prevent straight lines from becoming jaggy in the direction perpendicular to the direction of main scanning. However, though making straight lines less jaggy, printed images sometimes become grainy in color printing due to minute misalignments affecting dots of various colors. It has so far been difficult to reduce such graininess in printed images with the aid of conventional correction methods.
An object of the present invention, which was devised in order to overcome the above-described shortcomings of the prior art, is to provide a technique for adjusting recording position misalignments in the direction of main scanning and reducing the graininess of images printed in color.
Aimed at partially addressing the above-described problems, the present invention entails setting an adjustment value designed to reduce dot formation misalignments in a direction of main scanning during a process in which a printing device provided with a plurality of monochromatic nozzle groups for ejecting ink drops having mutually different colors is used to print images by depositing ink drops on a print medium and to form dots while main scanning is performed to move the plurality of monochromatic nozzle groups and/or the print medium. For the printing, a plurality of first color patches are formed on a print medium with dots composed of two or more types of ink for a plurality of auxiliary adjustment values, respectively. The plurality of first color patches are designed to reproduce mutually identical colors. A second color patch is formed on a print medium using dots composed of two or more types of ink in a different color and/or different method from that of the plurality of first color patches. The adjustment value is selected from the plurality of auxiliary adjustment values on the basis of the plurality of first color patches and the second color patch. Adopting this approach makes it possible to set an adjustment value after comparing the graininess of color patches that differ in color and/or printing scheme. As a result, it is possible to adjust recording position misalignments in the direction of main scanning and to reduce the graininess of images printed in color.
The second color patch is preferably formed on the print medium by a printing scheme different from that adopted for the plurality of first color patches, when the second color patch is formed. The second color patch reproduces the same color as that adopted for the plurality of first color patches. Adopting this approach makes it easier to select an adjustment value capable of yielding higher quality during printing by various printing schemes because a color patch with the same reproduction color is printed using a different printing scheme.
The plurality of first color patches are preferably formed by bidirectional printing, when the first color patch is formed. The second color patch is preferably formed by unidirectional printing, when the second color patch is formed. A dot formation misalignment brought about by bidirectional printing does not appear during unidirectional printing. With this arrangement, therefore, a first color patch in which bidirectional printing induces only a minimal dot formation misalignment can be easily selected by comparing a first color patch obtained by bidirectional printing and a second color patch obtained by unidirectional printing.
It is preferable that gray is selected as a color of the plurality of first color patches and the second color patch. Adopting this arrangement allows adjustment values to be set by conducting a comprehensive assessment of the effect of dot misalignments affecting on the color inks used for color printing.
When the second color patch is formed, a plurality of second color patches for reproducing mutually identical colors are preferably formed at positions aligned in the direction of main scanning in relation to the plurality of first color patches. With this arrangement, the area occupied by first and second misalignment verification patterns on a print medium can be provided with smaller dimensions in the direction perpendicular to the direction of main scanning.
When the second color patch is formed, a plurality of second color patches may be formed on the print medium using the plurality of auxiliary adjustment values by the same printing scheme as the one used to print the plurality of first color patches. The plurality of second color patches may be designed to reproduce mutually identical colors and may be colored differently than the plurality of first color patches. Adopting this arrangement allows adjustment values to be set with consideration for the print quality of different color images. In this arrangement, the plurality of second color patches may be formed at positions aligned in the direction of main scanning in relation to the plurality of first color patches.
It is preferable that each of the first color patches are formed over at least one fourth of a printable area on the print medium in a direction perpendicular to the direction of main scanning. It is also preferable that the second color patch is formed over at least one fourth of the printable area on the print medium in the direction perpendicular to the direction of main scanning. Adopting this arrangement allows adjustment values to be set with consideration for dot formation misalignments that vary in the direction perpendicular to the direction of main scanning on a print medium.
It is preferable that the first color patches are formed over at least half of a printable area on the print medium in the direction of main scanning. It is also preferable that the second color patch is formed over at least half of the printable area on the print medium in the direction of main scanning. Adopting this arrangement allows adjustment values to be set with consideration for dot formation misalignments that vary in the direction of main scanning on a print medium.
The present invention can be implemented as the following embodiments.
(1) Adjustment value determination methods, printing methods, and printing control methods.
(2) Printing devices and print control devices.
(3) Computer programs for operating such devices or performing such methods.
(4) Storage media containing computer programs for operating such devices or performing such methods.
(5) Data signals having the form of carrier waves and containing computer programs for operating such devices or performing such methods.